In widely known secondary batteries for purposes such as driving a motor vehicle, an electricity-generating element assembly includes an electricity-generating element group with a positive electrode plate and a negative electrode plate arranged via separators, and an electrolyte wetting the electricity-generating element group. The electricity-generating element assembly is housed in a closed-end metallic battery casing, and an opening in this battery casing is sealed off with a metallic battery cover. Lithium-ion secondary batteries are typical such batteries.
Traditionally known rectangular lithium-ion secondary batteries each include: a rectangularly parallelepipedic closed-end battery casing having an open end (opening) of a substantially rectangular shape; a battery cover for sealing off the open end; and an electricity-generating element group constructed into a flat shape to match the shape of a space defined by the battery casing and the battery cover. In secondary batteries of this kind, terminals for connection to the outside of the battery are mounted on the battery cover so as to be exposed on the outside and are electrically connected to the electricity-generating element group, within the battery casing, by an electrically conductive member.
To mount the terminals on the battery cover, it is necessary to ensure electrical insulation between both and airtightness between spatial clearances. In order to satisfy these requirements, the secondary battery disclosed in Patent Document 1, for example, includes a battery casing and terminals having a connecting plane perpendicular to a principal plane of a battery cover, the battery casing and the terminals being placed at relative positions in a mold and then formed by injection molding with a sealing material (resin).